Method of coating metal articles.



R. J. SHOEMAKER METHOD OF COATING METAL ARTICLES.

APPLICATION FlLED JULY 5.1917.

1 276,977, Patented Aug. 27, 1918.

* as as mass easier.

ROBERT JAY SHOEMAKEB, F TOPEKA, KANSAS.

METHOD OF COATING METAL ARTICLES.

. To all whom it may concern:

Be it known that I, ROBERT J. SHoE- MAKER, a citizen of the United States, residing at Topeka, in the county of Shawnee and State of Kansas, have invented certain new and useful Improvements in,Methods of Coating Metal Articles, of which the following is a specification.

My invention relates to the art of coating or latin metal articles with a metal of a di erent ind, and the objectof the inven- "tionis to provide certain improvements in this art whereby the operation in question is performed more economically, conveniently and efiiciently than has been possible heretofore.

A more specific object of the invention is to improve upon the method of lead-plating metal articles disclosed in the patent to Me- Clintock and Shoemaker, No, 1,195,376, patented August 22, 1916, I although the improvements of my present invention are not necessarily limited to the lead-plating process described and claimed in the patent referred to. It will be convenient, nevertheless, to describe the present invention as a development of or improvement upon the patented process.

In employing the process described In the above mentioned patent in the lead-plating of boiler fines and other articles, I have made the discovery that if, instead of usingzinc chlorid alone as a flux, a certain amount of common salt (sodium chlorid) is mixed with the zinc chlorid, a flux is obtained which has a melting point approximately fifty to seventy degrees Fahrenheit lower than a flux composed of pure zinc chlorid. The fact that these two salts, when mixed and subjected to heat, have a lower melting oint than either of them alone (the melting point of zinc chlorid is about 540 Fahrenheit and the melting point of common salt about 1500 Fahrenheit) is of considerableim ortance in the matter of the choice of a flux or the treatment-of the metal article preliminary to submerging in the bath of plating metal, in a process, such as that disclosed in the patent, where the flux floats on the bath ofplating metal. At the ord1- nary working temperatures the flux composed of zinc chlorid and sod um chlorid, due probably to its lower melting point, is thinner and more oily in its character than a flux composed of zinc chlorid alone. Melting at a lower temperature, the flux can be Specification of Letters Patent. Pa fijgnted A 27 1913 Application fil'ed July 5,

1917. a Serial No. 178,728

more easily kept from scaling and hardenmg. Asa result, the plating metal adheres more firmly to the article 'bein plated and the coatlng is more certain to be free from imperfections and porosity. The accompanying drawing shows diagrammatically a preferred form of apparazinc chlorid and sodium chlorid I do not mean to imply that the ingredients of the flux remain chemically unchanged when the point of fusion is reached. At this temperature there may be some dissociation and possibly a. combination of the chemical elements of the two salts. As to'this I express no opinion. The important fact, so far as my present invention is concerned, is that the melting point of the two salts, when mixed together is considerably lower than the melting point of either of them separately. The body of flux is retained to any suitable depth on the bath of plating metal C by meansof a suitable frame E.

The metal article to be plated is first preferably pickled in muriatic acid, particularly if the article be composed of steel or iron, to remove oxids from its surface, and is then immersed in the body of flux D. It is then loweredinto the body of coating metal C. I have found by experiment that with lead as a coatin metal the best results are obtained when t e temperature of the bath is maintained at about 700 Fahrenheit.

Some difiiculty was experienced in the lead-plating operation above described due to the formation of lead oxids on the surface of the hath not covered by flux D. The bath had to be continually skimmed and the loss of the platin metal on this account was considerable." I the oxide are not removed they are likely to adhere to the plated article to the detriment of the coating thereon. This diificulty has been overcome 'by covering the portion of the surface of the bath outside of the frame E with a thin film F of the flux. This flux, when made of a mixture of zinc chlorid and sodium chlorid, is so thin and oily that when the plating bath is covered with a stratum of the flux of a thickness of hall an inch, for exam le, it will not adhere to the plated article w en the latter is withdrawn from the bath. This thin film of the flux protects the plating metal from contact with the air and prevents the oxidation thereof.

I claim:

1. Improvement in the method or plating metal articles which consists in immersing the article in a flux composed of zinc chlorid and common salt in a molten state and thereafter in a bath of molten plating metal.

2. Improvement in the method of plating metal articles which consists in immersing the article in a flux composed of substantially eighty per cent., by weight, of zinc chlorid and twenty per cent. of common salt in a molten state, and thereafter immersing the article in a bath of molten plating metal.

3. improvement in the method of plating metal articles which consists in introducing the article into a bath of molten plating metal through a supernatant body of flux containing zinc chlorid and common salt in a molten state.

l. improvement in the method of leadplating metal articles which consists in immersing the article in a flux composed of zinc chlorid and common salt in a molten state and thereafter introducing the same into a bath 0:5 molten lead.

5. improvement in the method of leader atent? plating metal articles which consists in introducing the article into a loath of molten lead through a supernatant body of flux containing zinc chlorid and common salt in a molten state.

6. Improvement in the method of leadplating metal articles which consists in introducing the article into a bath oI molten lead through a supernatant body of flux composed of substantially eighty per cent, by weight, of zinc chlorid and twenty per cent. of common salt in a molten state.

'7. lmprovei'nent in the method of plating metal articles which consists in introducing the article into a bath of molten plating metal through a supernatant body of flux containing zinc chlorid and common salt in molten state, said body of flux covering only a portion of the surface of the plating metal and covering the remaining surface of the plating metal with a relatively thin film of the fiuX.

8. improvement in the method of leadplating metal articles which consists in introducing the article into a bath of molten lead through a supernatant body of flux containing zinc chlorid and common salt which covers only a portion of the surface of the body of lead, and covering the remaining surface of the body of lead with a relatively thin film of the flux,

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